A shell mold process, which is a casting mold making method that involves filling, in a preheated die, resin-coated sand having molding sand coated with phenol resin etc. and then thermosetting the resin, is widely used in the field of foundry. As the molding sand serving as aggregate for resin-coated sand, silica sand is widely used, but because of its indefinite shape and inferior fluidity, there is a limit to cope with filing in a core shape increasingly complicated in recent years. Further, because silica sand is highly thermally expansible, it is problematic in respect of dimensional accuracy.
As a means to solve these problems, use of spherical molding sand produced by granulation-sintering has also been proposed, but the resulting molding sand is porous with low sphericity. Accordingly, this molding sand, when formed into resin-coated sand, is poor in fluidity and filling properties and inferior in an effect of improving the roughness of the surface of cast metal. For improvement in this respect, JP-A 2003-251434 proposes that a molten material is air-pulverized to produce spherical molding sand, and this spherical molding sand attains higher sphericity and smoother surface than those of molding sand produced by the sintering method, but is still unsatisfactory. JP-A 2004-202577 discloses spherical molding sand produced by a flame fusion method, and describes a molding method wherein the spherical molding sand is combined with furan resin and alkali phenol resin.